ben: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/ben - from package: ben

You may install the required package with command apt-get install {package}
Error in other languages:
ben: bevel nie gevind nie
ben: comandă negăsită
ben: comando não encontrado
ben: commande introuvable
ben: command not found
ben: käsku ei ole
ben: không tìm thấy lệnh
ben: komanda nerasta
ben: Kommando nicht gefunden.
ben: kommandot finns inte
ben: komut yok
ben: nie znaleziono polecenia
ben: níor aimsíodh an t-ordú
ben: no se encontró la orden
ben: no s'ha trobat l'ordre
ben: opdracht niet gevonden
ben: parancs nem található
ben: perintah tidak ditemukan
ben: príkaz nenájdený
ben: příkaz nenalezen
ben: команда не найдена
ben: командата не е открита
ben: 命令找不到
ben: コマンドが見つかりません